From 25844ff728e4a0e5430ba2032457aba7b780a701 Mon Sep 17 00:00:00 2001
From: Jorge Ramirez-Ortiz <jorge@foundries.io>
Date: Fri, 15 Apr 2022 11:46:47 +0200
Subject: [PATCH] feat(bl31): aarch64: RESET_TO_BL31_WITH_PARAMS

It is not always the case that RESET_TO_BL31 enabled platforms don't
execute a bootloader before BL31.

For those use cases, being able to receive arguments from that first
loader (i.e: a DTB with TPM logs) might be necessary feature.

This code has been validated on iMX8mm.

Signed-off-by: Jorge Ramirez-Ortiz <jorge@foundries.io>
Change-Id: Ibf00c3867cb1d1012b8b376e64ccaeca1c9d2bff
---
 Makefile                       | 2 ++
 bl31/aarch64/bl31_entrypoint.S | 4 +++-
 make_helpers/defaults.mk       | 3 +++
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index da3e4931e..ebeb5ed4c 100644
--- a/Makefile
+++ b/Makefile
@@ -996,6 +996,7 @@ $(eval $(call assert_booleans,\
         PROGRAMMABLE_RESET_ADDRESS \
         PSCI_EXTENDED_STATE_ID \
         RESET_TO_BL31 \
+        RESET_TO_BL31_WITH_PARAMS \
         SAVE_KEYS \
         SEPARATE_CODE_AND_RODATA \
         SEPARATE_BL2_NOLOAD_REGION \
@@ -1127,6 +1128,7 @@ $(eval $(call add_defines,\
         PSCI_EXTENDED_STATE_ID \
         RAS_EXTENSION \
         RESET_TO_BL31 \
+        RESET_TO_BL31_WITH_PARAMS \
         SEPARATE_CODE_AND_RODATA \
         SEPARATE_BL2_NOLOAD_REGION \
         SEPARATE_NOBITS_REGION \
diff --git a/bl31/aarch64/bl31_entrypoint.S b/bl31/aarch64/bl31_entrypoint.S
index ed058648f..b0c46dc7b 100644
--- a/bl31/aarch64/bl31_entrypoint.S
+++ b/bl31/aarch64/bl31_entrypoint.S
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2021, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2022, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -67,6 +67,7 @@ func bl31_entrypoint
 		_exception_vectors=runtime_exceptions		\
 		_pie_fixup_size=BL31_LIMIT - BL31_BASE
 
+#if !RESET_TO_BL31_WITH_PARAMS
 	/* ---------------------------------------------------------------------
 	 * For RESET_TO_BL31 systems, BL31 is the first bootloader to run so
 	 * there's no argument to relay from a previous bootloader. Zero the
@@ -77,6 +78,7 @@ func bl31_entrypoint
 	mov	x21, 0
 	mov	x22, 0
 	mov	x23, 0
+#endif /* RESET_TO_BL31_WITH_PARAMS */
 #endif /* RESET_TO_BL31 */
 
 	/* --------------------------------------------------------------------
diff --git a/make_helpers/defaults.mk b/make_helpers/defaults.mk
index 99f44a4ec..eb58b36a8 100644
--- a/make_helpers/defaults.mk
+++ b/make_helpers/defaults.mk
@@ -254,6 +254,9 @@ RAS_EXTENSION			:= 0
 # By default, BL1 acts as the reset handler, not BL31
 RESET_TO_BL31			:= 0
 
+# By default, clear the input registers when RESET_TO_BL31 is enabled
+RESET_TO_BL31_WITH_PARAMS	:= 0
+
 # For Chain of Trust
 SAVE_KEYS			:= 0